Hi everyone,
I’m making a first-person video game and I’m relatively new with Blender and animating. I’ve made an arm and I rigged it, the first idle animation I made turned out okay, as well as my second animation…
However, now I’m having issues I’ve never seen before. The fingers have longish nails and the nail on the middle finger now decided to start bending along with the rest of the finger?
It hasn’t done that before, what am I doing wrong? I’ve uploaded some screenshots and the file in case anyone could help out.

You can upload a Blender file herehttp://pasteall.org/blend/ and post the URL if need be. Without seeing the file, I would guess that you have weighted some of the vertexes with another bone. Here is how you can check. Be sure you have checked both boxes on your armature modifier (display modifier in edit mode and also adjust cage). Go into pose mode and pose the armature with the problem. Then select your mesh and go into edit mode. Select a “bad” vertex and check your vertex weights in the N panel to see if you have other bones influencing your weight paint.

Usually when a mesh suffers from unexpected deforms you have a vertex weight contamination issue—things like the first bone of the finger having a tiny amount of weight on the fingernails area when only the last bone should have influence there.

Did you auto weighted it? Without looking at the file, my advice is:

Prepare the mesh for re-weighting

Make sure IK control bones, poles and anything that only acts as a control for other bones have “Deform” unchecked at Bone Properties > Deform

Make sure you don’t have extra bones in the area you want to rig, including hidden bones

Delete all armature-related vertex groups

Place the armature in Rest Pose

Now you can enter Weight Paint Mode, select all bones, auto weight again

Hi! Thank you too, for replying and for giving such detailed instructions
I tried auto-weighting but it did a terrible job so I painted everything myself. Turning off bone deform leaves everything to look okay except for the middle finger and its nail, which are the making the issue.
I checked my vertexes like @stilltrying said and I can’t see anything wrong. I uploaded the file, I’d really appreciate it if you could take a look at it: http://pasteall.org/blend/index.php?id=53117

Yeah, you got weight paint issues. Example: There are index finger bones weighted to the tip of the middle finger.

If you select each one of these vertex groups, go into edit mode, select the middle finger and press “Remove” to remove them this fingernail will stop acting up. But this is not the only finger with weight issues.

I’m also learning rigging and one thing I noticed is that usually auto weight doesn’t work well when either the armature is not positioned correctly/has too few bones or the mesh has topology issues. Common issues are not creating a mesh well-positioned for rigging or using too few edge loops at joints.

Good topology for a good rest pose is one where fingers, eyelids, mouth are as wide apart as possible so auto weight doesn’t accidentally pick geometry it’s not supposed to pick. In your case that means keeping fingers well apart and palm of hand splayed. It also has as few “baked-in” joint deforms as possible: straight fingers, straight spine, straight neck, all joints bent only enough to make sure they bend in the correct direction once rigged. The first post of this WIP thread of mine is a good example of someone committing both mistakes at once.

Also, use at least 3 edge loops in joints so they can keep their shape when deforming:

The middle edge (highlighted in blue) will keep the volume while the other two loops will do the actual bending.

And try to make your bones touch the tip of whatever they’re controlling. Your fingertip bones don’t go all way to the tips of the nails.

A good armature will have joints where where joint loops are. Fingers are easy, select the middle edge loop of a joint, place the cursor to selected (space bar + Snap cursor to selected), go into edit mode for the armature, select the respective bone head/tail overlap and place them at the 3D cursor location.

Because I’m using auto weight as a learning tool sometimes the model doesn’t have enough bones to keep shape when deforming. Example: I’ll leave just a spine bone and a breathing control bone in the thorax of this model, but in real life you’d have an entire ribcage there.

Because it’s a very large boneless area auto weighting leads to the thorax picking weights from shoulder and wing bones. So I created two temporary bones (children to the spine) in the place a group of real bones would be. In the end I’ll assign the weight of these bones to the spine and delete them.

@skuax Being new to all of this sometimes I have trouble remembering proper terminology, and not being a native English speaker doesn’t help. So when in a hurry I make stuff up.

I’ve no words, you made a video explanation! Thank you so, very much, it was incredibly informative and helpful!! I’m a rookie with weight painting and rigging, I had no idea Zero Weights even existed. I looked at the hand at least a dozen times, I was almost going insane.
I didn’t use automatic weights, I try but most of the time I’m not happy with what it does, so I just start from scratch.
Again, thank you so much!
And I’m terribly sorry it took me a while to reply, my online university studies started and this week was a mess.
Thank you thank you

Jesus Christ I have so much to learn. Your crow is absolutely gorgeous by the way, I read the post you linked. Turns out there was a pixel wide weight on the nail which was linked with a random bone which I couldn’t see because Zero Wights was off hahah
Wonderful post though, I thought the fingers were far way enough, I’ll definitely keep that in mind for the future ! Thank you so much for replying though and for providing me with so much new info, I really appreciate it If you have any tutorials to suggest, please do paste some links